Treatment effects and lip profile changes following premolars extraction treatment vs fixed functional treatment in Class II division 1 malocclusion: A randomized controlled clinical trial

ABSTRACT Objective: The objective of this two-arm parallel randomized controlled trial was to evaluate the treatment effects and lip profile changes in skeletal Class II patients subjected to premolars extraction treatment versus fixed functional treatment. Methods: Forty six subjects fulfilling inclusion criteria were randomly distributed into Group PE (mean age 13.03±1.78 years) and Group FF (mean age 12.80±1.67 years) (n=23 each). Group PE was managed by therapeutic extraction of maxillary first premolars and mandibular second premolars, followed by mini-implant-supported space closure; and Group FF, by fixed functional appliance therapy. Skeletal, dental, and soft-tissue changes were analyzed using pre and post-treatment lateral cephalograms. Data obtained from this open label study was subjected to blind statistical analysis. Results: Extraction treatment resulted in greater increase of nasolabial angle (NLA: 3.1 [95% CI 2.08, 4.19], p<0.001), significant improvement of upper lip (UL-E line: -2.91 [95% CI -3.54, -2.28], p<0.001, UL-S line: -2.50 [95% CI -2.76, -2.24], p<0.001, UL-SnPog’: -2.32 [95% CI -2.90, -1.74], p<0.01) and lower lip position (LL-E line: -0.68 [95% CI -1.36, 0.00], p<0.01, LL-S line: -0.55 [95% CI -1.11, 0.02], p<0.01, and LL-SnPog’: -0.64 [95% CI -1.20, -0.07], p<0.01), lip thickness (UL thickness: 2.27 [95% CI 1.79, 2.75], p<0.001; LL thickness: 0.41 [95% CI -0.16, 0.97], p<0.01), upper lip strain (UL strain: -2.68 [95% CI -3.32, -2.04], p<0.001) and soft tissue profile (N’-Sn-Pog’: 2.68 [95% CI 1.87, 3.50], p<0.01). No significant difference was observed between the groups regarding skeletal changes in the maxilla and mandible, growth pattern, overjet, overbite, interincisal angle and soft tissue chin position (p>0.05). Premolar extraction treatment demonstrated significant intrusion-retraction of maxillary incisors, better maintenance of maxillary incisor inclination, and significant mandibular molar protraction; whereas functional treatment resulted in retrusive and intrusive effect on maxillary molars, marked proclination of mandibular anterior teeth, and significant extrusion of mandibular molars. Both treatment modalities had similar treatment duration. Implant failure was seen in 7.9% of cases, whereas failure of fixed functional appliance was observed in 9.09% of cases. Conclusions: Premolar extraction therapy is a better treatment modality, compared to fixed functional appliance therapy for Class II patients with moderate skeletal discrepancy, increased overjet, protruded maxillary incisors and protruded lips, as it produces better dentoalveolar response and permits greater improvement of the soft tissue profile and lip relationship.


INTRODUCTION
Class II malocclusion is a frequent condition, with a prevalence of around 30% of the patients seeking orthodontic treatment. 1 This malocclusion has a variety of manifestations, which encompass dental, skeletal and soft tissue components. In Class II malocclusion, relative position of teeth affects the overjet, overbite and overlying soft tissues, which in turn influences the patients' facial esthetics and quality of life. 2 Depending on the underlying condition, multiple treatment strategies are available for the management of Class II malocclusion. 3 Premolar extraction treatment routinely enables retraction of maxillary anterior teeth and optimization of overjet. There is a dichotomy among researchers regarding the effects of premolar extraction on esthetics of soft tissue profile. It is believed that reduction in dental volume secondary to extractions hampers the lip support. 4 Though, extraction treatment has shown to be detrimental to facial profile and overbite, and strong arguments are being made against the use of this protocol 5 -although existing scientific literature disavows these claims. [6][7][8][9] Treatment by both fixed and removable functional appliances is effective in correcting the Class II malocclusion. 10 The masking of underlying skeletal discrepancy by functional treatment is mainly due to transient rather than additional bony growth. 11 Kochar GD, Londhe S, Chopra SS, Kohli S, Kohli VS, Kamboj A, Verma M -Treatment effects and lip profile changes following premolars extraction treatment vs fixed functional treatment in Class II division 1 malocclusion: A randomized controlled clinical trial Orthopedic management primarily produces dentoalveolar changes, with limited skeletal effects. Contradictory results regarding the effect of fixed functional appliance on soft tissues have been reported in literature. 12,13 The last decade has witnessed a steady upsurge in the interest for facial esthetics. Therefore, soft tissues changes following orthodontic treatment are given more importance than ideal occlusion. Presently, data is lacking on the relationship of soft tissue profile changes and both treatment modalities, with and without extractions. 14 The present study endeavors to contribute to the existing knowledge base. This prospective randomized clinical trial was conducted with the aim to compare the treatment effects and lip profile changes in skeletal Class II patients subjected to premolar extractions and those treated with fixed functional appliance therapy. The null hypothesis was that there would be no statistically significant difference in treatment outcome and profile change of patients with Class II malocclusion treated with extraction of premolars and those treated with fixed functional appliance therapy.

TRIAL DESIGN AND SETTING
This study was conducted as a two-arm parallel randomized to previously published studies. 15 Considering certain amount of dropouts, a greater number of subjects was selected.

PARTICIPANTS AND ELIGIBILITY CRITERIA
Patient selection and follow-up were conducted in accordance with CONSORT guidelines (Fig 1). Recruitment      to monitor treatment changes. Skeletal (n=14), dental (n=13) and soft tissue (n= 3) measurements were recorded, to determine the changes produced by the treatment (Fig 2) (Supplementary Tables 1 and 2). Horizontal plane -HP (7° to SN plane) and vertical plane -VP (plane perpendicular to HP passing though Sella) were used as reference planes, similar to previous studies. 16 The secondary outcome included skeletal and dental treatment changes, overall treatment duration and overall failure rate of implants / fixed functional appliance.  Table 1 and Supplementary Table 2 for definitions of landmarks and cephalometric parameters). SNB The inferior posterior angle between SN and NB 5.
FMA Angle formed between ANS PNS and GoMe 6.
SN -GoGn Angle formed between SN and GoGn 7. IMPA Angle formed between long axis of most prominent mandibular central incisor and GoMe 8.
ANB Angle formed by the intersection of NA and NB 9.
N -A -Pog Angle formed between NA and APog

10.
Interincisal angle Angle formed between long axis of most prominent maxillary central incisor and mandibular central incisor 11.
A -VP Perpendicular distance between point A and VP 12.
N -ANS Perpendicular distance between ANS and HP 13.
N -PNS Perpendicular distance between PNS and HP 14.
U1 -VP Perpendicular distance between incisal tip of U1 and VP 15.
U1 -HP Perpendicular distance between incisal tip of U1 and HP 16.
U6 -VP Perpendicular distance between incisal tip of U6 and VP 17.
U6 -HP Perpendicular distance between incisal tip of U6 and HP 18.
CoGn Linear distance between Co and Gn 21.
GoPog Linear distance between Go and Pog 22.
L1 -VP Perpendicular distance between incisal tip of L1 and VP 23.
L6 -VP Perpendicular distance between incisal tip of L6 and VP 25.
B' -VP Perpendicular distance between B' and VP 27.
Pog' -VP Perpendicular distance between Pog' and VP

28.
Overjet Distance between the incisal edges of the maxillary and mandibular central incisors, parallel to the occlusal plane 29.
Overbite Distance between the incisal edges of the maxillary and mandibular central incisors, perpendicular to the occlusal plane 30.
NLA Angle formed by Cl, Sn, and Ls 31. UL

INTERIM ANALYSES AND STOPPING GUIDELINES
Not applicable.

BLINDING
It was not feasible to blind for the clinical procedures. Blinding was done for statistical analysis only.

ERROR OF THE METHOD AND STATISTICAL ANALYSIS
Ten cephalograms were randomly selected and retraced after a two-weeks interval, to determine the intra and inter-operator reliability. Allocation of all the traced cephalograms was done by a random list created online (https://www.random.org/). The reliability of recorded measurements was determined using intraclass correlation coefficient (ICC): ICC closer to 1 indicated highly reliable measurement.  (Fig 3).
ICC of intra-examiner and inter-examiner measurements was 0.96 and 0.92, respectively, depicting highly reliable measurements.
The Student t-tests comparing the pretreatment parameters and the treatment changes between the groups are presented in Tables 2 to 5. With regard to the soft tissue changes (Fig 4), treatment effects were evident on almost all cephalometric parameters (Table 3)       With regard to the skeletal changes (Table 4)  With regard to the dentoalveolar changes (Table 5)

APPLIANCE / IMPLANT FAILURE
The implant failure rate was 7.9% -i.e., only 7 of the total implants placed became loose. Failure of the functional appliance was reported in 3 cases: One of the subjects had recurrent breakages of the functional appliance spring and was thus excluded from the present study.

Successful orthodontic treatment is not just about establish-
ing a static as well as dynamic occlusal relationship, but also to achieve an esthetic soft tissue profile. 17 Over the years, an Ideally, the subjects of a trial should demonstrate no difference in characteristics prior to the treatment, as phenotypic differences may influence the response to growth and treatment mechanics. 20 Closely matched groups of mixed Indian population with no difference in distribution in terms of age, gender and cephalometric parameters -i.e., moderate skeletal discrepancy, increased overjet, protruded maxillary incisors-were selected and investigated in the present study (Tables 1 and 2).
Severity of sagittal molar relationship directly influences the amount of retraction in Class II cases; hence, considering it during a trial was proposed in a systematic review. 21 In the present trial, subjects with at least ¾ Class II molar and canine relationship were included.
Soft tissue response secondary to aging and treatment assists clinician in planning the best suited treatment for the patient.  (Table 3). With regard to the dentoalveolar changes, highly significant differences were observed between the two treatment strate- in extraction cases, contrary to the present findings. Despite the similar extraction pattern, difference in findings could be attributable to differences in anchorage mechanisms.
Both treatment modalities reduced the overjet and the overbite to normal limits, with almost similar proportional correction. In Group PE, overall change of overjet and overbite was -4.23mm and -2.64mm, respectively; whereas Group FF demonstrated reduction of -4.73mm and -3.27mm, respectively. Similar changes were reported by Janson et al. 23 Optimization of overjet in both groups was mainly due to dentoalveolar changes.
In Group FF, it was mainly attributable to retroclination of max-

illary incisors and proclination of mandibular incisors, whereas
in Group PE, en-masse retraction as well as retroclination of maxillary incisor was attributed for the major change.
Treatment duration is one of the major factors influencing satisfaction among patients undergoing orthodontic treatment. 36 There was no significant difference in overall treatment duration between the two groups, which is not in agreement with the findings of Janson et al, 37 who reported premolar extraction treatment to be significantly shorter than non-extraction therapy. Difference in findings may be attributable to the use of extraoral headgear for correcting sagittal discrepancy. Mini-implants were used in Group PE in order to optimize the maxillary anterior teeth retraction and mandibular molar protraction. A recent systematic review 38 refutes any significant advantages of using absolute anchorage in conjunction with fixed functional appliances, hence the same was not planned for Group FF.
Highly promising overall success rate of mini-implants (86.5%) was reported by a meta-analysis. 39 In the present study, overall failure rate was 7.9%, i.e., only 7 implants of the total implants placed became loose, which is in agreement with previously published data. 39 Four failures were reported on maxillary left side, two on the mandibular left side, and one on maxillary right side. There was no discontinuation of the treatment, as failed implants were retrieved and repositioned.
Forsus TM failure rate of 37% has been reported in literature. 40 Failure of Forsus TM was encountered in three cases of the present study: Two of them reported breakage of the spring and one reported loss of slit crimp. Broken spring and lost crimp were replaced in the mentioned cases. Since one of these two cases had recurrent breakages of the spring, this case was excluded from the study. The higher failure rate of Bowman et al 40 may be attributable to the varying experience level of the practitioners.
None of the participants asked to be removed from the study, reflecting acceptance of both treatment modalities.

GENERALIZABILITY
The results can be generalized to the average patient of most orthodontic clinical settings, as the present study was conducted in orthodontic departments of a government institute, based on broad inclusion criteria, and treatments were performed by experienced clinicians.

CONCLUSION
The null hypothesis of this study was rejected. Management by extraction of premolars is a better treatment modality than functional treatment for managing skeletal Class II division 1 malocclusion in Class II subjects with moderate skeletal discrepancy, increased overjet, protruded maxillary incisors and protruded lips.
1. Both treatment modalities resulted in significant dentoalveolar changes; however, inclination of maxillary as well as mandibular incisors was better maintained in premolar extraction treatment.
2. Lip position relative to nose and chin, as well as nasolabial angle, improved significantly in maximum anchorage premolar extraction treatment cases.